Embodiments of the present invention relate generally to a filtering system, and more specifically to a self-powered active electromagnetic interference (EMI) filter for a pulse width modulated (PWM) inverter.
Typically, a PWM inverter is employed in motor drive units used in applications such as aviation systems, submarines, oil and gas extraction systems, and the like. In the PWM inverter, the switches are continuously activated and deactivated according to a predetermined pattern. A fast change in voltage and current of the PWM inverter occurs due to continuous activation and deactivation of the switches of the PWM inverter. As a result, high frequency harmonic components are generated due to the fast change in voltage and current. The generation of the high frequency harmonic components leads to motor failure and electromagnetic interferences. In addition, common mode noise is generated at both alternating current (AC) side and direct current (DC) side of the PWM inverter.
Typically, passive filters are employed in order to filter the common mode noise generated in the PWM inverter. However, such passive filters are costly and add considerable weight and size to the PWM inverter due to the use of inductors and capacitors. For aviation applications, it is desirable to use devices/filters having considerably lower weight.
Currently, in some applications, for example, aviation applications, an active EMI filter is employed for filtering the common mode noise of the PWM inverter. Such active EMI filters have a comparably lower weight, are compact, and provide a higher power density as compared to passive filters. However, the active EMI filter employs an external power supply source for powering the components. The use of external power supply source for the active EMI filter creates an additional electrical loop through which noise signals may be introduced. Further, the use of the external power supply source establishes a need for a grounding path. Such a grounding path may allow for generated signals to leak, thereby compromising the filtering capability of the active EMI filter. Moreover, the conventional active EMI filters are used to reduce the common mode noise of only one side of the PWM inverter, i.e. either the AC side or the DC side. The reduction of noise at only one side causes common mode noise at the other side of the PWM inverter to increase considerably.